Compact Coarse Wavelength Division Multiplexing (CWDM) has been widely deployed in Telecom, such as Metro core network and Metro access network, for multiple wavelength signals transportation in the network so as to increase the bandwidth, due to its compact dimension and advantages in term of low insertion loss and low temperature dependent loss.
On the other hand, a tapping function is very important for a flexible and versatile network having monitoring and debugging functions in nowadays high speed network due to greatly increased video demand, social networking, big data, and cloud computing. Traditionally, fused couplers are used to perform the tapping function. The tapping function to meet the increasingly higher speed requirement (for example above 10 Gbps) needs low mode dispersion in the optical transportation network. In this scenario, fused couplers cannot fulfill the requirement. Fused couplers suffer from mode dispersion in a high speed network.
Furthermore, a fused coupler typically performs uni-directional tapping. For uni-directional tapping, the signal flow direction is fixed in the network. In multiplexing and demultiplexing, the signal flow directions are opposite to each other. Multiplexing and demultiplexing modes are not exchangeable in a uni-directional CWDM network. However, multiplexing and demultiplexing modes are exchangeable in a bi-directional (BiDi) CWDM network. In nowadays flexible and versatile networks, a BiDi CWDM network having bi-directional tapping is greatly needed. Accordingly, bi-directional and low-dispersion or dispersionless taps for BiDi CWDM are in demand. In the disclosure, low-dispersion refers to low mode dispersion, and dispersionless refers to mode-dispersionless.
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